This invention relates to an improvement in the soles of sport shoes suitable for use in track races (such as short-, medium- and long-distance races) and marathon races, as well as in the training therefor.
In the tract and marathon races or the training therefor, moving actions of a runner exert an extremely great load on the sole, in particular at the heel portion, of shoes that he wears. It is generally considered that a load three times as much as the body weight of a runner (shoes wearer) is exerted on the heel of the sole upon running movement and, in jumping movement, the load applied on the heel at the shoe sole amounts to about 5-6 times as much as the body weight of a jumper.
Conventional sport shoes for such racing and training uses have a sole comprising a sponge rubber elastic body. Such a sole is, for example, entirely formed with a sponge rubber elastic body of one or more layers, or composed of three layers of sponge rubber whose interlayer sole is formed at its heel with a space in which air is confined tightly.
The former sole is, however, defective since sponge rubber having a sufficient elasticity and durability to withstand the foregoing large load can not easily be available. The latter sole having an air inclusion layer for tightly confining air therein in the heel of the interlayer sole also has a defect in that while a resilience capable of withstanding the foregoing load can be attained due to the resilience of air in the air inclusion layer in addition to the elasticity of the sponge rubber per se, the air present in the air inclusion layer destructs its surrounding wall thereby damaging the interlayer sole upon repeated exertion of the load on the sole during use.